1. Field of the Invention
This invention relates to improvements in an intermediate optical device interposed removably between a camera body and an interchangeable lens.
2. Description of the Prior Art
Conventionally, intermediate optical devices of the subject type include an extension ring which is constructed so as to take a close-up photograph by increasing the amount of working separation between an interchangeable lens and the film, and a rear converter which includes an inside lens and is constructed so as to change the focal length by combining the inside lens with the interchangeable lens. Each of these intermediate optical devices includes a rear end mount connected to a camera body by a relative turning operation, and a front end mount connected to the interchangeable lens by a relative turning operation so as to be adapted to be inserted removably between the camera body and the interchangeable lens. Most of them include an automatic diaphragm interlock mechanism which mechanically couples the automatic diaphragm stopping down mechanism of the camera body and the diaphragm stopping down mechanism of the interchangeable lens corresponding to the automatic exposure function of the camera.
Recently, a camera having an automatic focusing mechanism has appeared. This results in an intermediate optical device which includes an automatic focusing interlock mechanism which mechanically couples a drive output shaft connected to a motor within the camera body to a follower shaft to operate the focusing lens within the interchangeable lens.
However, an intermediate device including an automatic mechanical diaphragm interlock mechanism, as mentioned above, produces more or less "play" and/or "deflection" in the interlock mechanism. If such device is interposed between the camara body and the interchangeable lens, it cannot avoid a slight decrease in the accuracy of the diaphragm aperture due to a decrease in the positional accuracy and dynamic characteristics of the respective components constituting the interlock mechanism. The inertia of the interlock mechanism will produce some delay in the diaghragm stopping down operation. These decreases in accuracy cannot be completely eliminated. Thus in design, manufacturing accuracy is established at a predetermined level sufficient for achieving an exposure error within a predetermined tolerance such as the film latitude on the assumption that only one such intermediate optical device is interposed. However, if the user interposes between the camera body and the interchangeable lens a plurality of interconnected intermediate optical devices against the designer's intention, a decrease in the accuracy of the diaphragm aperture and a delay in the diaphragming operation would increase accumulatively and the exposure error would exceed the desired tolerance.
If a plurality of intermediate optical devices including an automatic mechanical focusing interlock mechanism, as described above, are interconnected, a problem in strength occurs in that the automatic focusing interlock mechanism and its driving system are overloaded thereby being damaged.
This invention contemplates the above problems. It is an object of this invention to provide an intermediate optical device which can be freely coupled to the camera body and/or the interchangeable lens, but prevents an erroneous interconnection of a plurality of intermediate optical devices even if it is attempted.